Heat developable light-sensitive materials forming a photographic image according to a heat developing method are disclosed in, for example, U.S. Pat. Nos. 3,152,904 and 3,457,075 and D. Morgan and B. Shely, "Thermally Processed Silver Systems" (Imaging Processes and Materials), Neblette, 8th ed., compiled by Sturge, V. Walworth and A. Shepp, page 2 (1969).
The heat developable light-sensitive material contains a silver source (e.g., organic silver salt) capable of reduction, a photocatalyst (e.g., silver halide) in an amount of catalytic activity, a color toner for controlling silver tone and a reducing agent, which are usually dispersed in a binder matrix. The heat developable light-sensitive material is stable at room temperature, however, when it is heated at a high temperature (e.g., 80.degree. C. or higher) after exposure, silver is produced through an oxidation-reduction reaction between a silver source (which functions as an oxidizing agent) capable of reduction and a reducing agent. The oxidation-reduction reaction is accelerated by the catalytic action of a latent image generated upon exposure. Silver produced by the reaction of an organic silver salt in the exposure region provides a black image in contrast to the non-exposure region, thereby forming an image.
The above-described heat developable light-sensitive material has been used as a microphotographic light-sensitive material or for X-ray photographing. However, it is being used only partly as a light-sensitive material for printing. This is because the image obtained is low in Dmax and soft in gradation and the image quality is very bad as a light-sensitive material for printing.
On the other hand, recently, laser or light emission diode has been developed and scanner or image setter having an oscillation wavelength in the region of from 600 to 800 nm has been popularized. As a result, light-sensitive materials having adaptability to these output apparatuses and having high sensitivity, high Dmax and satisfactory contrast are being strongly demanded. Also, demands for simple processing and dry processing are increasing.
U.S. Pat. No. 3,667,958 describes a heat developable light-sensitive material using a polyhydroxybenzene and a hydroxylamine, a reductone or a hydrazine in combination and states that this material can show high image discriminability and high resolution. However, the combination with these reducing agents is found to readily cause increase of fogging.